In electrophotographic applications such as xerography, a charge retentive surface (i.e. photoconductor, photoreceptor, or imaging surface) is electrostatically charged, and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is well known, and useful for light lens copying from an original, and printing applications from electronically generated or stored originals, where a charged surface may be imagewise discharged in a variety of ways. Ion projection devices where a charge is imagewise deposited on a charge retentive substrate operate similarly.
Although a preponderance of the toner forming the image is transferred to the paper during transfer, some toner invariably remains on the charge retentive surface, it being held thereto by relatively high electrostatic and/or mechanical forces. Additionally, paper fibers, Kaolin and other debris have a tendency to be attracted to the charge retentive surface. It is essential for optimum operation that the toner remaining on the surface be cleaned thoroughly therefrom.
A commercially successful mode of cleaning employed in automatic xerographic devices utilizes a brush with soft conductive fiber bristles which have suitable triboelectric characteristics. While the bristles are soft they are sufficiently firm to remove residual toner particles from the charge retentive surface. A voltage is applied to the fibers to enhance removal of toner from the charge retentive surface.
However, not all toner and debris is removed from the surface by the brush cleaner. It has been found that toner particles agglomerate with themselves, and with certain types of debris to form a spot-wise deposition that can eventually strongly adhere to the charge retentive surface. These spots range from 50 .mu.m to 500 .mu.m in diameter, but typically are about 200 .mu.m in diameter. The agglomerate particles range in material compositions from strictly toner to a broad assortment of toner, and plastics and debris from paper. The spots cause a copy quality defect showing up as a black spot on a background area of the copy which is the same size as the spot on the photoreceptor. The spot on the copy varies slightly with the exact machine operating conditions, but cannot be deleted by control of the the machine process characteristics. The presence of agglomerate spots tends to be particularly predominant with the use of recycled-content paper in a reproduction apparatus, as more paper debris is often present on recycled-content paper than on non-recycled content paper. Also, the need for effective agglomerate spot removal may be more critical with use of recycled-content paper because preexisting spots often appear on the surface of this type of paper which remain after the image has been transferred. In studying the formation of these spots, it was noted that most of the spots appeared instantaneously on the charge retentive surface, i.e., most spots were not the result of a continuing nucleation process. It was subsequently noted that newly deposited spots were more weakly adhered to the surface than older spots.
Agglomerate spot cleaning blades ("spots blades") have been used for removal of agglomerate particles from a charge retentive surface, wherein a relatively lower load is applied to the blade so that the various problems associated with the frictional sealing contact that must occur in the normal cleaning engagement of blades with a charge retentive surface are avoided.
Upon insertion of a new blade into an electrophotographic device, however, high frictional forces are noted during a break in period, until the blade is properly lubricated. A fixed blade is prone to "tuck" under during break in, or startup, because the dynamic friction forces established between the moving photoreceptor and blade create a bending moment which further increases the normal force on the blade. Blade tuck is predominant when the blade is in the doctoring or scraper mode where the cleaning blade edge acts to scrape, or "shear" agglomerate particles from the photoconductive belt surface.
When blade tuck occurs, the increased force on the blade results in increased pressure of the blade on the photoconductive belt, causing wear marks and scratches on the charge retentive surface. These deleterious effects of blade tuck reduce the life expectancy of the photoconductive belt or the spots blade. For example, testing of reproduction apparatus having an agglomerate spot cleaning blade (without incorporation of the present invention) and where blade tuck had occurred, has shown to reduce the number of cycles before photoreceptor belt failure from 500,000 to 50,000. The occurrence of blade tuck also results in an increased necessity for unscheduled maintenance due to either photoreceptor belt failure, blade failure, or by machine failure which may occur, particularly if a separate or lower power drive motor is used on the photoreceptor belt.
The following disclosures may be relevant to various aspects of the present invention and may be briefly summarized as follows:
U.S. Pat. No. 4,989,047 issued to Jugle et al. discloses an apparatus for cleaning an electrophotographic printer imaging surface. The cleaning apparatus includes a primary cleaner device in combination with a secondary cleaning device. The secondary cleaning device consists of a blade holder pivotally connected to the housing. The blade holder holds a cleaning blade in frictional contact with the imaging surface, arranged at a low angle of attack and to which a relatively low load is applied for the removal of toner and other debris agglomerates.
U.S. Pat. No. 5,031,000 issued to Pozniakas is a Continuation-In-Part of U.S. Pat. No. 4,989,047, and discloses a floating support assembly which enables the secondary cleaning blade to float relative to the charge retentive surface. This floating support assembly is loaded with a weight selected to maintain the blade in contact with the charge retentive surface, and has a stop to limit the range of movement of the floating blade, so that blade creep is prevented. Blade creep is defined as the tendency of the blade to slide under the loading weight to a position where the angle of attack is approximately 0.degree., and is no longer effective.
U.S. Pat. No. 5,168,309 issued to Adachi et al. discusses the problem of blade "burring" (described as a force tending to turn up the edge of the blade) on a cleaning blade and especially on a contact charging blade (used for charging the photosensitive member in place of a corona discharger), and its negative effect on the attempt of the contact charging blade to achieve uniformity of charge over the surface of an image bearing member. This patent proposes a contact charging blade wherein the frictional coefficient of that portion of the blade which contacts the photosensitive member is at a decreased level so that burring of the blade is prevented. To accomplish this objective, the following alterations to the blade composition and characteristics are disclosed: a sheet layer of low friction coefficient material attached to the contact side of the contact charging blade; a finely roughened contact side of a molded, conductive rubber blade surface which reduces the contact surface area of the blade to the photosensitive member; and a molded, conductive rubber blade surface, wherein a parting agent remaining on the contact side of the blade has lubricating property and is utilized to reduce the frictional coefficient of the blade with respect to the photosensitive member.